Synthesis of Four Coordinated Palladium Complexes and Their Applications in Light Emitting Devices Thereof

ABSTRACT

Synthesis of four coordinated palladium complexes and their applications in light emitting devices thereof.

BACKGROUND

1. Technical Field

The present disclosure relates to palladium complexes which are capableof absorbing and/or emitting light and are thus useful as an emissive orabsorption material in a device.

2. Technical Background

Compounds capable of absorbing and/or emitting light are ideally suitedfor use in a wide variety of optical and electro-optical devices,including photo-absorbing devices such as solar and photo-sensitivedevices, photo-emitting devices, such as organic light emitting diodes(OLEDs), or devices capable of both photo-absorption and emission. Muchresearch has been devoted to the discovery and optimization of organicand organometallic materials for use in optical and electro-opticaldevices. Generally, research in this area aims to accomplish a number ofgoals, including improvements in absorption and emission efficiency, aswell as improvements in processing ability, among others.

Despite significant advances in research devoted to optical andelectro-optical materials, many current devices comprising organic ororganometallic materials have yet to be optimized. Many materialscurrently used in optical and electro-optical devices have a numberdisadvantages, including poor processing ability, inefficient emissionor absorption, and less than ideal stability, among others. Thus, a needexists for new materials which exhibit improved performance in opticaland electro-optical devices. This need and other needs are satisfied bythe compositions and methods of the present invention.

SUMMARY

The present invention relates to palladium complexes that exhibitphoto-absorption and photo-emission, to methods of making suchcompounds, and to applications thereof, including optical devicescomprising the compounds.

In one embodiment, the compounds are represented by the formula:

wherein each R¹ and R² in (R¹)₂ and (R²)₂ independently representshydrogen, optionally substituted C₁-C₄ alkyl, halogen, hydroxyl, amino,nitro, or thiol;

R³ represents methyl, ethyl, propyl, or butyl;

Y^(1a) represents O, S, NR^(4a), wherein R^(4a) represents optionallysubstituted C₁-C₄ alkyl; Si(R^(4b))₂, wherein each R^(4b) in (R^(4b))₂independently represents optionally substituted C₁-C₄ alkyl; orC(R^(4c))₂, wherein each R^(4c) in (R^(4c))₂ represents hydrogen oroptionally substituted C₁-C₄ alkyl;

n is an integer 0 or 1;

Y^(1b), when present, represents O, S, NR^(5a), wherein R^(5a)represents optionally substituted C₁-C₄ alkyl; Si(R^(5b))₂, wherein eachR^(5b) in (R^(5b))₂ independently represents optionally substitutedC₁-C₄ alkyl; or C(R^(5c))₂, wherein each R^(5c) in (R^(5c))₂ representshydrogen or optionally substituted C₁-C₄ alkyl;

each of Y^(2a), Y^(2b), Y^(2c), and Y^(2d) independently represents N,NR^(6a), or CR^(6b), wherein each of R^(6a) and R^(6b) independentlyrepresents hydrogen, optionally substituted C₁-C₄ alkyl, halogen,hydroxyl, amino, nitro, or thiol;

each of Y^(3a), Y^(3b), Y^(3c), Y^(3d), Y^(3e), Y^(4a), Y^(4b), Y^(4c),and Y^(4d) independently represents N, O, S, NR^(6a), CR^(6b), whereineach of R^(6a) and R^(6b) independently represents hydrogen oroptionally substituted C₁-C₄ alkyl; or Z(R^(6c))₂, wherein Z is C or Si,and wherein each R^(6c) in (R^(6c))₂ independently represents hydrogenor optionally substituted C₁-C₄ alkyl;

wherein m is an integer 1 or 2;

wherein the open dotted circle

indicates partial or full unsaturation of the ring with which it isassociated;

provided that if m is 1, each of Y^(2a) and Y^(2d) is CH and each ofY^(2b) and Y^(2c) is N, then at least one of Y^(4a), Y^(4b), Y^(3a), orY^(3d) is not N; and

provided that if n is 0, m is 2, each of Yea and Y^(2d) is CH, and eachof Y^(2b) and Y^(2c) is N, then at least one of Y^(3b) or Y^(3c) is notN.

Also disclosed are optical devices, such as organic light emittingdevices and luminescent display devices that comprise one or morecompounds of the invention as a functional material, such as alight-emitter or absorber, or both.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, which are incorporated in and constitute apart of this specification, illustrate several aspects and together withthe description serve to explain the principles of the invention.

FIG. 1 is a drawing of a cross-section of an exemplary organiclight-emitting diode (OLED).

FIG. 2 is a photoluminescence spectrum produced from a specificembodiment, 2-(3-(pyridin-2-yl)phenoxy)-6-(pyridin-2-yloxy)phenyl]Pd(II)(Pd003) taken in degassed dichloromethane at room temperature, whereinthe quantum yield was about 0.1 and the luminescence lifetime was about11 μsec. The chemical structure of Pd003 is also illustrated in theinset.

FIG. 3 is a photoluminescence spectrum produced from a specificembodiment, 2-(3-(pyridin-2-yl)phenoxy)-6-(pyridin-2-yloxy)phenyl]Pd(II)(Pd003) doped into a polymethylmethacrylate (PMMA) thin film at roomtemperature, which shows a thin film photoluminescence quantum yieldover 70%.

FIG. 4 illustrates (A) a specific embodiment, and (B) aphotoluminescence spectrum of the same in a solution of dichloromethane,obtained at room temperature wherein the quantum yield was about 0.16and the luminescent lifetime was about 30 μsec.

FIG. 5 illustrates (A) a specific embodiment, (B) an electroluminescentspectrum from a OLED device comprising the specific embodiment, (C) aplot of external quantum efficiency vs. current density for a Pd003based device, and (D) a current vs. voltage plot at a 1% doping level.

Additional aspects of the invention will be set forth in part in thedescription which follows, and in part will be obvious from thedescription, or can be learned by practice of the invention. Theadvantages of the invention will be realized and attained by means ofthe elements and combinations particularly pointed out in the appendedclaims. It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only and are not restrictive of the invention, as claimed.

DESCRIPTION

The present invention can be understood more readily by reference to thefollowing detailed description of the invention and the Examplesincluded therein.

Before the present compounds, devices, and/or methods are disclosed anddescribed, it is to be understood that they are not limited to specificsynthetic methods unless otherwise specified, or to particular reagentsunless otherwise specified, as such can, of course, vary. It is also tobe understood that the terminology used herein is for the purpose ofdescribing particular aspects only and is not intended to be limiting.Although any methods and materials similar or equivalent to thosedescribed herein can be used in the practice or testing of the presentinvention, example methods and materials are now described.

As used in the specification and the appended claims, the singular forms“a,” “an” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a component”includes mixtures of two or more components.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, another aspect includes from the one particular value and/orto the other particular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another aspect. It will be furtherunderstood that the endpoints of each of the ranges are significant bothin relation to the other endpoint, and independently of the otherendpoint. It is also understood that there are a number of valuesdisclosed herein, and that each value is also herein disclosed as“about” that particular value in addition to the value itself. Forexample, if the value “10” is disclosed, then “about 10” is alsodisclosed. It is also understood that each unit between two particularunits are also disclosed. For example, if 10 and 15 are disclosed, then11, 12, 13, and 14 are also disclosed.

As used herein, the terms “optional” or “optionally” means that thesubsequently described event or circumstance can or can not occur, andthat the description includes instances where said event or circumstanceoccurs and instances where it does not.

The term “alkyl” as used herein is a branched or unbranched saturatedhydrocarbon group of 1 to 24 carbon atoms, such as methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-pentyl,isopentyl, s-pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl,dodecyl, tetradecyl, hexadecyl, eicosyl, tetracosyl, and the like. Thealkyl group can be cyclic or acyclic. The alkyl group can be branched orunbranched. The alkyl group can also be substituted or unsubstituted.For example, the alkyl group can be substituted with one or more groupsincluding, but not limited to, optionally substituted alkyl, cycloalkyl,alkoxy, amino, ether, halide, hydroxy, nitro, silyl, sulfo-oxo, orthiol, as described herein. A “lower alkyl” group is an alkyl groupcontaining from one to six (e.g., from one to four) carbon atoms.

The terms “amine” or “amino” as used herein are represented by theformula NA¹A²A³, where A¹, A², and A³ can be, independently, hydrogen oroptionally substituted alkyl, cycloalkyl, alkenyl, cycloalkenyl,alkynyl, cycloalkynyl, aryl, or heteroaryl group as described herein.

The term “halide” as used herein refers to the halogens fluorine,chlorine, bromine, and iodine.

The term “hydroxyl” as used herein is represented by the formula —OH.

The term “nitro” as used herein is represented by the formula —NO₂.

The term “nitrile” as used herein is represented by the formula —CN.

The term “thiol” as used herein is represented by the formula —SH.

Disclosed are the components to be used to prepare the compositions ofthe invention as well as the compositions themselves to be used withinthe methods disclosed herein. These and other materials are disclosedherein, and it is understood that when combinations, subsets,interactions, groups, etc. of these materials are disclosed that whilespecific reference of each various individual and collectivecombinations and permutation of these compounds can not be explicitlydisclosed, each is specifically contemplated and described herein. Forexample, if a particular compound is disclosed and discussed and anumber of modifications that can be made to a number of moleculesincluding the compounds are discussed, specifically contemplated is eachand every combination and permutation of the compound and themodifications that are possible unless specifically indicated to thecontrary. Thus, if a class of molecules A, B, and C are disclosed aswell as a class of molecules D, E, and F and an example of a combinationmolecule, A-D is disclosed, then even if each is not individuallyrecited each is individually and collectively contemplated meaningcombinations, A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F are considereddisclosed. Likewise, any subset or combination of these is alsodisclosed. Thus, for example, the sub-group of A-E, B-F, and C-E wouldbe considered disclosed. This concept applies to all aspects of thisapplication including, but not limited to, steps in methods of makingand using the compositions of the invention. Thus, if there are avariety of additional steps that can be performed it is understood thateach of these additional steps can be performed with any specificembodiment or combination of embodiments of the methods of theinvention.

Throughout the specification, it should be understood that where lettersand/or symbols are utilized to represent atoms or functional groups, andwherein multiple instances of the same letter and/or symbol are present,that each individual instance can represent the same or differentspecies (e.g., atom and/or functional group) than any other instanceusing the same letter and/or symbol. Similarly, when a metal is depictedas a portion of a chemical structure, the notation can refer to a singlemetal atom and/or to a plurality of atoms. In one aspect, a notation fora metal refers to a single metal atom. In another aspect, a notation fora metal refers to a plurality of metal atoms.

In one aspect, the invention comprises phosphorescent multidentate, forexample, tridentate and/or tetradentate, palladium (II) complexes. Inanother aspect, such multidentate palladium complexes can be modifiedand/or specifically tailored to tune the emission spectra from, forexample, ultraviolet to near-infrared emission. In yet another aspect,the inventive compositions can provide improved stability and efficiencyover conventional light emitting materials. In yet other aspects, theinventive compositions can be useful as luminescent labels, absorbers,emitters, or a combination thereof.

In one aspect, the inventive compositions are represented by the generalformula:

wherein Ar1, Ar2, Ar3, and Ar4, if present, represent aromatic groups,wherein each E represents an optional linking atom, such as, forexample, carbon or oxygen, and wherein R, if present, represents anancillary ligand

In various aspects, an ancillary ligand can comprise one or more of thefollowing:

wherein, R¹-R¹⁰ of the ancillary ligand each independently represent ahydrogen atom, an alkyl group, a haloalkyl group, an aralkyl group, analkenyl group, an alkynyl group, an aryl group, an amino group, a mono-or di-alkylamino group, a mono- or diaryl amino group, an alkoxy group,an aryloxy group, a heteroaryloxy group, an alkoxycarbonyl group, anacyloxy group, an acylamino group, an alkoxycarbonylamino group, anaryloxycarbonylamino group, a sulfonylamino group, a sulfamoyl group, acarbamoyl group, an alkylthio group, a sulfinyl group, a ureido group, aphosphoramide group, a hydroxyl group, amercapto group, a halogen atom,a cyano group, a sulfo group, a carboxyl group, a nitro group, ahydrazino group, a substituted silyl group, or a polymerizable group;further, wherein a plurality of Rs exist, the number of R should be from0 to about 4, and each R can be the same or different from any other R.In one aspect, an ancillary ligand can comprise a hydrogen atom. Inanother aspect, an ancillary ligand can comprise an alkyl group. Inanother aspect, an ancillary ligand can comprise a haloalkyl group. Inanother aspect, an ancillary ligand can comprise a aralkyl group. Inanother aspect, an ancillary ligand can comprise a alkenyl group. Inanother aspect, an ancillary ligand can comprise an alkynl group. Inanother aspect, an ancillary ligand can comprise an aryl group. Inanother aspect, an ancillary ligand can comprise an amino group. Inanother aspect, an ancillary ligand can comprise an alkoxy group, anaryloxy group, a heteroaryloxy group, an alkoxycarbonyl group, anacyloxy group, or a combination thereof. In other aspects, an ancillaryligand can comprise an acylamino group, an alkoxycarbonylamino group, anaryloxycarbonylamino group, a sulfonylamino group, a sulfamoyl group, acarbamoyl group, an alkylthio group, a sulfinyl group, a ureido group, aphosphoramide group, a hydroxyl group, amercapto group, a halogen atom,a cyano group, a sulfo group, a carboxyl group, a nitro group, ahydrazino group, a substituted silyl group, a polymerizable group, or acombination thereof.

In still other aspects, an ancillary ligand can comprise a group orgroups difference from those specifically recited herein, and thepresent invention is not intended to be limited to any particularancillary ligand.

In various aspects, specific non-limiting examples of the inventivecomposition can be grouped and illustrated by ligand class. In oneaspect, the inventive composition can be represented by the generalformula:

wherein Pd represents palladium, each N represents a nitrogensubstituted aromatic group, each E represents an optional linking atom,such as, for example, carbon or oxygen, X represents a halogen or otherelectronegative group, and C represents an aromatic group. Specificexamples of inventive compositions within this ligand class cancomprise:

or a combination thereof.

In one aspect, the inventive composition can be represented by thegeneral formula:

wherein Pd represents palladium, each N represents a nitrogensubstituted aromatic group, each E represents an optional linking atom,such as, for example, carbon or oxygen, X represents a halogen or otherelectronegative group, and C represents an aromatic group. Specificexamples of inventive composition within this ligand class can comprise:

or a combination thereof.

In one aspect, the inventive composition can be represented by thegeneral formula:

wherein Pd represents palladium, each N represents a nitrogensubstituted aromatic group, each E represents an optional linking atom,such as, for example, carbon or oxygen, and X represents a halogen orother electronegative group. Specific examples of inventive compositionwithin this ligand class can comprise:

or a combination thereof.

In one aspect, the inventive composition can be represented by thegeneral formula:

wherein Pd represents palladium, N represents a nitrogen substitutedaromatic group, each E represents an optional linking atom, such as, forexample, carbon or oxygen, X represents a halogen or otherelectronegative group, and each C represents an aromatic group. Specificexamples of inventive composition within this ligand class can comprise:

or a combination thereof.

In one aspect, the inventive composition can be represented by thegeneral formula:

wherein Pd represents palladium, each E represents an optional linkingatom, such as, for example, carbon or oxygen, R represents an ancillaryligand, and each C represents an aromatic group. Specific examples ofinventive composition within this ligand class can comprise:

or a combination thereof.

In one aspect, the inventive composition can be represented by thegeneral formula:

wherein Pd represents palladium, each N represents a nitrogensubstituted aromatic group, each E represents an optional linking atom,such as, for example, carbon or oxygen, and each C represents anaromatic group. Specific examples of inventive composition within thisligand class can comprise:

or a combination thereof.

In one aspect, the inventive composition can be represented by thegeneral formula:

wherein Pd represents palladium, each N represents a nitrogensubstituted aromatic group, each E represents an optional linking atom,such as, for example, carbon or oxygen, and each C represents anaromatic group. Specific examples of inventive composition within thisligand class can comprise:

or a combination thereof.

In one aspect, the inventive composition can be represented by thegeneral formula:

wherein Pd represents palladium, N represents a nitrogen substitutedaromatic group, each E represents an optional linking atom, such as, forexample, carbon or oxygen, and each C represents an aromatic group.Specific examples of inventive composition within this ligand class cancomprise:

or a combination thereof.

In one aspect, the inventive composition can be represented by thegeneral formula:

wherein Pd represents palladium, N represents a nitrogen substitutedaromatic group, each E represents an optional linking atom, such as, forexample, carbon or oxygen, and each C represents an aromatic group. Aspecific example of an inventive composition within this ligand classcan comprise:

In one aspect, the inventive composition can be represented by thegeneral formula:

wherein Pd represents palladium, each N represents a nitrogensubstituted aromatic group, each E represents an optional linking atom,such as, for example, carbon or oxygen, and C represents an aromaticgroup. Specific examples of inventive compositions within this ligandclass can comprise:

or a combination thereof.

In one aspect, the inventive composition can be represented by thegeneral formula:

wherein Pd represents palladium, each N represents a nitrogensubstituted aromatic group, each E represents an optional linking atom,such as, for example, carbon or oxygen, and C represents an aromaticgroup. A specific example of an inventive composition within this ligandclass can comprise:

In another aspect, the compounds of the present invention arerepresented by the formula:

In the above formula, each R¹ and R² in (R¹)₂ and (R²)₂ independentlyrepresents hydrogen, optionally substituted C₁-C₄ alkyl, halogen,hydroxyl, amino, nitro, or thiol; Y^(1a) represents O, S, NR^(4a),wherein R^(4a) represents optionally substituted C₁-C₄ alkyl;Si(R^(4b))₂, wherein each R^(4b) in (R^(4b))₂ independently representsoptionally substituted C₁-C₄ alkyl; or C(R^(4c))₂, wherein each R^(4c)in (R^(4c))₂ represents hydrogen or optionally substituted C₁-C₄ alkyl;n is an integer 0 or 1; Y^(1b), when present, represents O, S, NR^(5a),wherein R^(5a) represents optionally substituted C₁-C₄ alkyl;Si(R^(5b))₂, wherein each R^(5b) in (R^(5b)), independently representsoptionally substituted C₁-C₄ alkyl; or C(R^(5c))₂, wherein each R^(5c)in (R^(5c))₂ represents hydrogen or optionally substituted C₁-C₄ alkyl;each of Y^(2a), Y^(2b), Y^(2c), and Y^(2d) independently represents N,NR^(6a), or CR^(6b), wherein each of R^(6a) and R^(6b) independentlyrepresents hydrogen, optionally substituted C₁-C₄ alkyl, halogen,hydroxyl, amino, nitro, or thiol; each of Y^(3a), Y^(3b), Y^(3c),Y^(3d), Y^(3e), Y^(4a), Y^(4b), Y^(4c), and Y^(4d) independentlyrepresents N, O, S, NR^(6a), CR^(6b), wherein each of R^(6a) and R^(6b)independently represents hydrogen or optionally substituted C₁-C₄ alkyl;or Z(R^(6c))₂, wherein Z is C or Si, and wherein each R^(6c) in(R^(6c))₂ independently represents hydrogen or optionally substitutedC₁-C₄ alkyl; m is an integer 1 or 2; wherein the open dotted circle

indicates partial or full unsaturation of the ring with which it isassociated.

In one embodiment of the formula above, if m is 1, each of Y^(2a) andY^(2d) is CH and each of Y^(2b) and Y^(2c) is N, then at least one ofY^(4a), Y^(4b), Y^(3a), or Y^(3d) is not N. For example, according tothis embodiment, the following compound is not included in the aboveformula:

As can be seen in the preceding example above, m is 1, each of Y^(2a)and Y^(2d) is CH and each of Y^(2b) and Y^(2c) is N; however, each ofY^(4a), Y^(4b), Y^(3a), or Y^(3d) is N. It follows that the precedingexample, according to this embodiment, is not included within thegeneral formula above. In the practice of this embodiment, similaranalysis can be used to determine whether or not a compound is or is notincluded within the general formula above.

In a further embodiment of the general formula above, if n is 0, m is 2,each of Y^(2a) and Y^(2d) is CH, and each of Y^(2b) and Y^(2c) is N,then at least one of Y^(3b) or Y^(3c) is not N. For example, accordingto this embodiment, the following compound is not included in the aboveformula:

As can be seen in the preceding example above, n is 0, m is 2, each ofY^(ea) and Y^(2d) is CH, and each of Y^(2b) and Y^(2c) is N. However,each of Y^(3b) and Y^(3c) is N. It follows that the preceding example,according to this embodiment, is not included within the general formulaabove. Once more, in the practice of this embodiment, similar analysiscan be used to determine whether or not a compound is or is not includedwithin the general formula above.

In one embodiment of the general formula above, the compound isrepresented by the formula:

Non-limiting examples of specific embodiments within this formulainclude:

In another embodiment of the general formula above, the compound isrepresented by the formula:

Non-limiting examples of specific embodiments within this formulainclude:

In another embodiment of the general formula above, the compound isrepresented by the formula:

Non-limiting examples of specific embodiments within this formulainclude:

In another embodiment of the general formula above, the compound isrepresented by the formula:

Non-limiting examples of specific embodiments within this formulainclude:

In another embodiment of the general formula above, the compound isrepresented by the formula:

Non-limiting examples of specific embodiments within this formulainclude:

In another embodiment of the general formula above, the compound isrepresented by the formula:

Non-limiting examples of specific embodiments within these formulainclude:

In other aspects, any one or more of the general formulas and/orspecific examples recited herein can be excluded from the invention. Forexample, in one aspect, the formula

is not included in the present invention.

The compounds of the invention can be made using a variety of methods.In one embodiment, wherein Y^(1a) is O, the compounds can be providedaccording to Scheme 1.

With reference to Scheme 1, step “a” can be accomplished, for example,by using a catalytic amount of a coupling reagent, such as Cu₂O, whichcouples alcohols, particularly phenols, with halogenated phenyl groups.The variable “X” in Scheme 1 above represents a halogen (i.e., Cl, F, I,Br), and is preferably I when used in conjunction with Scheme 1.

Each side of a ligand which complexes a metal can be made independentlyusing a variety of methods, which, in one aspect, depend on whetherY^(3a) is N or C. With reference to Scheme 2 below, when Y^(4a) is N,the precursor can, in one aspect, be provided according to Scheme 2(A),wherein a halogenated phenyl compound is reacted with a pyrazole,imadazole, 1H-1,2,3-triazole, 1H-tetrazole, or 2H-pentazole. In such anaspect, the halogenated phenyl compound can comprise any halogen (X),including Cl, Br, F, or I, but is preferably I, which is typically morereactive in a coupling reaction. The halogenated phenyl compound andcorresponding pyrazole, imadazole, 1H-1,2,3-triazole, 1H-tetrazole, or2H-pentazole can be coupled using a metallic and/or organometalliccoupling agent, such as, for example, Cu₂O. During such a couplingreaction, it can, in one aspect, be advantageous to include an acidscavenger, such as, for example, syn-2-pyridinealdoxime, in a smallmolar ratio, for example, about 20 mol %.

In another aspect, when Y^(4a) is C, a different protocol can be used toprovide the precursor. With reference to Scheme 2(B) below, ahalogenated phenyl, as discussed above can be reacted with a tetrazole,1,2,3-triazole, pyrazole, or pyrrole to achieve a carbon-carbon bondcoupling, as opposed to a carbon-nitrogen bond coupling as shown inScheme 2(A). In one aspect, the carbon-carbon bond coupling can also beachieved using an organometallic catalyst, such as, for example, aPd(II) catalyst (e.g., Pd(OAc)₂) in a small molar ratio. In one aspect,such an organometallic catalyst can optionally be used together with anexcess of a salt mixture, such as KI and/or CuI. As one of skill in theart can appreciate, when employing each of the coupling reactions shownin Scheme 2, it can, in various aspects, be advantageous to perform thereactions in a dry atmosphere, for example under argon, or even in a drybox to minimize and/or avoid moisture or oxygen inclusion.

In one aspect, the compounds of the invention can be useful in a varietyof optical applications. When utilized as light emitting materials, theinventive compounds can be useful in organic light emitting diodes(OLED)s, luminescent devices and displays, and/or other light emittingdevices. With reference to FIG. 3, for example, a specific embodiment,2-(3-(pyridin-2-yl)phenoxy)-6-(pyridin-2-yloxy)phenyl]Pd(II) exhibitsphotoluminescence (absorption of light followed by emission of light)across a range of wavelengths, including a narrow blue emission andother emission bands out to the red to near-IR region of the spectrum.

The emission (and absorption) profile of the compounds can be tuned byvarying the structure of the ligand surrounding the metal center. Forexample, compounds having a ligand with electron withdrawingsubstituents can, in one aspect, generally exhibit different opticalproperties, including emission and absorption, than compounds having aligand with electron donating substituents. Generally, a chemicalstructural change can affect the electronic structure of the compound,thereby affecting the absorption and emission properties of thecompound. Thus, the compounds of the present invention can be tailoredor tuned to a specific application that desires a particular emission orabsorption characteristic. One of skill in the art, in possession ofthis disclosure, could readily design and/or select an appropriatemultidentate palladium compound, in accordance with the various aspectsdescribed herein, to use in a particular application.

In one embodiment, the compounds can be used in an OLED. FIG. 1illustrates a cross-sectional view of an exemplary OLED 100, whichincludes substrate 102 with an anode 104, which is typically atransparent material, such as indium tin oxide, a layer ofhole-transporting material(s) (HTL) 106, a layer of light processingmaterial 108, such as an emissive material (EML) including an emitterand a host, a layer of electron-transporting material(s) (ETL) 110, anda metal cathode layer 112.

In such an embodiment, the layer of light processing material 108 cancomprise one or more compounds of the present invention optionallytogether with a host material. The host material, if present, can be anysuitable host material known in the art. The emission color of an OLEDcan be determined by the emission energy (optical energy gap) of thelight processing material 108, which as discussed above can be tuned bytuning the electronic structure of the emitting compounds and/or thehost material. Both the hole-transporting material in the HTL layer 106and the electron-transporting material(s) in the ETL layer 110 cancomprise any suitable hole-transporter known in the art. A selection ofwhich is well within the purview of those skilled in the art.

It will be apparent that the compounds of the present invention canexhibit phosphorescence. Phosphorescent OLEDs (i.e., OLEDs withphosphorescent emitters) typically have higher device efficiencies thatother OLEDs, such as fluorescent OLEDs. Light emitting devices based onelectrophosphorescent emitters are described in more detail inWO2000/070655 to Baldo et al., which is incorporated herein by thisreference for its teaching of OLEDs, and in particular phosphorescentOLEDs.

EXAMPLES

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how thecompounds, compositions, articles, devices and/or methods claimed hereinare made and evaluated, and are intended to be purely exemplary of theinvention and are not intended to limit the scope of what the inventorsregard as their invention. Efforts have been made to ensure accuracywith respect to numbers (e.g., amounts, temperature, etc.), but someerrors and deviations should be accounted for. Unless indicatedotherwise, parts are parts by weight, temperature is in ° C. or is atambient temperature, and pressure is at or near atmospheric.

Example 1 Preparation of specific embodiment2-(3-(pyridin-2-yl)phenoxy)-6-(pyridin-2-yloxy)phenyl]Pd(II) Synthesisof 3-(pyridin-2-yloxy)phenol

Under a nitrogen atmosphere, a pressure vessel was charged with amagnetic stir bar, resorcinol (110 mmol), 2-bromopyridine (100 mmol),1-methylimidazole (5 mmol), and potassium carbonate (200 mmol). Pyridine(80 mL) was added and bubbled with nitrogen for 20 minutes beforecopper(I) iodide (10 mmol) was added and bubbled 10 minutes further. Thevessel was sealed and heated to 140° C. while stirring. After 2 days,the solution was allowed to cool. The solids were filtered off andrinsed with a 50:50 mixture of toluene and methanol. The filtrate wasreduced by rotary evaporation and 150 ml of water containing 10 mLglacial acetic acid was added and shaken vigorously. The water wasdecanted off and 50 mL of DCM was added, forming an off whiteprecipitate which was collected by vacuum filtration and dried withether, resulting in the pure product 3-(pyridin-2-yloxy)phenol with a55% yield. ¹H NMR (CDCl₃): 5.98 (s, 1H), 6.59 (s, 1H), 6.62-6.69 (m,2H), 6.94 (d, 1H), f 7.02 (dd, 1H), 7.23 (vt, 1H), 7.70 (dd, 1H), 8.23(b, 1H)

Synthesis of 2-(3-(3-bromophenoxy)phenoxy)pyridine

Under a nitrogen atmosphere, a pressure vessel was charged with amagnetic stir bar, 3-(pyridin-2-yloxy)phenol (50 mmol),2,6-dibromopyridine (50 mmol), 1-methylimidazole (25 mmol), andpotassium carbonate (100 mmol). Toluene (80 mL) was added and bubbledwith nitrogen for 20 minutes before copper(I) iodide (5 mmol) was addedand the solution bubbled for 10 minutes further. The vessel was sealedand heated to 140° C. while stirring. After 2 days, the solution wasallowed to cool and the solids were filtered off and rinsed withdichloromethane. The filtrate was added to a separatory funnelcontaining DCM and water. The water phase was washed 3 times with 75 mLDCM, and the combined organic layers were washed once with pure water.The organic layer was collected, dried with magnesium sulfate, filtered,and the filtrate reduced by rotary evaporation. The resulting oil waspurified by column chromatography using DCM over silica resulting in thepure product 2-(3-(3-bromophenoxy)phenoxy)pyridine with a 60% yield. ¹HNMR (CDCl₃): 6.80-6.85 (m, 2H), 6.91 (s, 1H), 6.94 (s, 1H), 6.97-7.03(m, 2H), 7.19 (vt, 1H), 7.21-7.24 (m, 2H), 7.36 (vt, 1H), 7.70 (dd, 1H),8.21 (dd, 1H).

Synthesis of 2-(3-(3-(pyridin-2-yl)phenoxy)phenoxy)pyridine

Under a nitrogen atmosphere, an oven dried three neck flask was chargedwith a magnetic stir bar, 2-(3-(3-bromophenoxy)phenoxy) (10 mmol), and2-(tripropylstannyl)pyridine (10 mmol). Dry toluene (100 mL) was addedand bubbled with nitrogen for 20 minutes beforeTetrakis(triphenylphosphine)palladium(0) (0.5 mmol) was added, bubbled10 minutes further, and brought to reflux for 2 days. After cooling, thecontents of the flask were filtered, the liquid reduced by rotaryevaporation, and the resulting oil was purified by column chromatographyusing DCM over silica to yield the pure product2-(3-(3-(pyridin-2-yl)phenoxy)phenoxy)pyridine with a 65% yield. ¹H NMR(CDCl₃): 6.84 (vt, 1H), 6.85-6.89 (m, 2H), 6.91 (d, 1H), 6.98 (dd, 1H),7.11 (dd, 1H), 7.24 (dd, 1H), 7.34 (vt, 1H), 7.44 (vt, 1H), 7.66-7.78(m, 5H), 8.19 (dd, 1H), 8.67 (dd, 1H).

Synthesis of[2-(3-(pyridin-2-yl)phenoxy)-6-(pyridin-2-yloxy)phenyl]Pd(II)

A mixture of 2-(3-(3-(pyridin-2-yl)phenoxy)phenoxy)pyridine (1 mmol),K₂PdCl₄ (1 mmol), and acetic acid (10 mL) was refluxed for 3 days. Themixture was allowed to cool to room temperature. The resulting whitecomplex was filtered off and washed with H₂O, MeOH, and Et₂O, and driedunder vacuum to2-(3-(pyridin-2-yl)phenoxy)-6-(pyridin-2-yloxy)phenyl]Pd(II). Theproduct was purified by sublimation for further testing.

What is claimed is:
 1. A compound represented by the formula:

wherein each R¹ and R² in (R¹)₂ and (R²)₂ independently representshydrogen, optionally substituted C₁-C₄ alkyl, halogen, hydroxyl, amino,nitro, or thiol; R³ represents methyl, ethyl, propyl, or butyl; Y^(1a)represents O, S, NR^(4a), wherein R^(4a) represents optionallysubstituted C₁-C₄ alkyl; Si(R^(4b))₂, wherein each R^(4b) in (R^(4b))₂independently represents optionally substituted C₁-C₄ alkyl; orC(R^(4c))₂, wherein each R^(4c) in (R^(4c))₂ represents hydrogen oroptionally substituted C₁-C₄ alkyl; n is an integer 0 or 1; Y^(1b), whenpresent, represents O, S, NR^(5a), wherein R^(5a) represents optionallysubstituted C₁-C₄ alkyl; Si(R^(5b))₂, wherein each R^(5b) in (R^(5b))₂independently represents optionally substituted C₁-C₄ alkyl; orC(R^(5c))₂, wherein each R^(5c) in (R^(5c))₂ represents hydrogen oroptionally substituted C₁-C₄ alkyl; each of Y^(2a), Y^(2b), Y^(2c), andY^(2d) independently represents N, NR^(6a), or CR^(6b), wherein each ofR^(6a) and R^(6b) independently represents hydrogen, optionallysubstituted C₁-C₄ alkyl, halogen, hydroxyl, amino, nitro, or thiol; eachof Y^(3a), Y^(3b), Y^(3c), Y^(3d), Y^(3e), Y^(4a), Y^(4b), Y^(4c), andY^(4d) independently represents N, O, S, NR^(6a), CR^(6b), wherein eachof R^(6a) and R^(6b) independently represents hydrogen or optionallysubstituted C₁-C₄ alkyl; or Z(R^(6c))₂, wherein Z is C or Si, andwherein each R^(6c) in (R^(6c))₂ independently represents hydrogen oroptionally substituted C₁-C₄ alkyl; wherein m is an integer 1 or 2;wherein the open dotted circle

indicates partial or full unsaturation of the ring with which it isassociated; provided that if m is 1, each of Y^(2a) and Y^(2d) is CH andeach of Y^(2b) and Y^(2c) is N, then at least one of Y^(4a), Y^(4b),Y^(3a), or Y^(3d) is not N; and provided that if n is 0, m is 2, each ofY^(2a) and Y^(2d) is CH, and each of Y^(2b) and Y^(2c) is N, then atleast one of Y^(3b) or Y^(3c) is not N.
 2. The compound of claim 1,which is represented by the formula:


3. The compound of claim 1, which is represented by the formula:


4. The compound of claim 1, which is represented by the formula:


5. The compound of claim 1, which is represented by the formula:


6. The compound of claim 1, which is represented by the formula:


7. An organic light-emitting diode (OLED) comprising, as an emissivematerial, a compound represented by the formula:

wherein each R¹ and R² in (R¹)₂ and (R²)₂ independently representshydrogen, optionally substituted C₁-C₄ alkyl, halogen, hydroxyl, amino,nitro, or thiol; R³ represents methyl, ethyl, propyl, or butyl; Y^(1a)represents O, S, NR^(4a), wherein R^(4a) represents optionallysubstituted C₁-C₄ alkyl; Si(R^(4b))₂, wherein each R^(4b) in (R^(4b))₂independently represents optionally substituted C₁-C₄ alkyl; orC(R^(4c))₂, wherein each R^(4c) in (R^(4c))₂ represents hydrogen oroptionally substituted C₁-C₄ alkyl; n is an integer 0 or 1; Y^(1b), whenpresent, represents O, S, NR^(5a), wherein R^(5a) represents optionallysubstituted C₁-C₄ alkyl; Si(R^(5b))₂, wherein each R^(5b) in (R^(5b))₂independently represents optionally substituted C₁-C₄ alkyl; orC(R^(5c))₂, wherein each R^(5c) in (R^(5c))₂ represents hydrogen oroptionally substituted C₁-C₄ alkyl; each of Y^(2a), Y^(2b), Y^(2c), andY^(2d) independently represents N, NR^(6a), or CR^(6b), wherein each ofR^(6a) and R^(6b) independently represents hydrogen, optionallysubstituted C₁-C₄ alkyl, halogen, hydroxyl, amino, nitro, or thiol; eachof Y^(3a), Y^(3b), Y^(3c), Y^(3d), Y^(3e), Y^(4a), Y^(4b), Y^(4c), andY^(4d) independently represents N, O, S, NR^(6a), CR^(6b), wherein eachof R^(6a) and R^(6b) independently represents hydrogen or optionallysubstituted C₁-C₄ alkyl; or Z(R^(6c))₂, wherein Z is C or Si, andwherein each R⁶ in (R^(6c))₂ independently represents hydrogen oroptionally substituted C₁-C₄ alkyl; wherein m is an integer 1 or 2;wherein the open dotted circle

indicates partial or full unsaturation of the ring with which it isassociated; provided that if m is 1, each of Y^(2a) and Y^(2d) is CH andeach of Y^(2b) and Y^(2c) is N, then at least one of Y^(4a), Y^(4b),Y^(3a), or Y^(3d) is not N; and provided that if n is 0, m is 2, each ofY^(2a) and Y^(2d) is CH, and each of Y^(2b) and Y^(2c) is N, then atleast one of Y^(3b) or Y^(3c) is not N.
 8. An organic photovoltaicdevice comprising, as a donor or acceptor material, a compoundrepresented by the formula:

wherein each R¹ and R² in (R¹)₂ and (R²)₂ independently representshydrogen, optionally substituted C₁-C₄ alkyl, halogen, hydroxyl, amino,nitro, or thiol; R³ represents methyl, ethyl, propyl, or butyl; Y^(1a)represents O, S, NR^(4a), wherein R^(4a) represents optionallysubstituted C₁-C₄ alkyl; Si(R^(4b))₂, wherein each R^(4b) in (R^(4b))₂independently represents optionally substituted C₁-C₄ alkyl; orC(R^(4c))₂, wherein each R^(4c) in (R^(4c))₂ represents hydrogen oroptionally substituted C₁-C₄ alkyl; n is an integer 0 or 1; Y^(1b), whenpresent, represents O, S, NR^(5a), wherein R^(5a) represents optionallysubstituted C₁-C₄ alkyl; Si(R^(5b))₂, wherein each R^(5b) in (R^(5b))₂independently represents optionally substituted C₁-C₄ alkyl; orC(R^(5c))₂, wherein each R^(5c) in (R^(5c))₂ represents hydrogen oroptionally substituted C₁-C₄ alkyl; each of Y^(2a), Y^(2b), Y^(2v), andY^(2d) independently represents N, NR^(6a), or CR^(6b), wherein each ofR^(6a) and R^(6b) independently represents hydrogen, optionallysubstituted C₁-C₄ alkyl, halogen, hydroxyl, amino, nitro, or thiol; eachof Y^(3a), Y^(3b), Y^(3c), Y^(3d), Y^(3e), Y^(4a), Y^(4b), Y^(4c), andY^(4d) independently represents N, O, S, NR^(6a), CR^(6b), wherein eachof R^(6a) and R^(6b) independently represents hydrogen or optionallysubstituted C₁-C₄ alkyl; or Z(R^(6c))₂, wherein Z is C or Si, andwherein each R^(6c) in (R^(6c))₂ independently represents hydrogen oroptionally substituted C₁-C₄ alkyl; wherein m is an integer 1 or 2;wherein the open dotted circle

indicates partial or full unsaturation of the ring with which it isassociated; provided that if m is 1, each of Y^(2a) and Y^(2d) is CH andeach of Y^(2b) and Y^(2c) is N, then at least one of Y^(4a), Y^(4b),Y^(3a), or Y^(3d) is not N; and provided that if n is 0, m is 2, each ofY^(2a) and Y^(2d) is CH, and each of Y^(2b) and Y^(2c) is N, then atleast one of Y^(3b) or Y^(3c) is not N.